#include<stdio.h>
int main() {
	int i, j;
	double sum1=0,sum2=0;
	for (i = 1;i <= 100;i+=2) {
		sum1 += 1.0 / i;
	}
	for (j = -2;j >= -100;j -= 2) {
		sum2 += 1.0 / j;
	}
	printf("%lf", sum1 + sum2);
	return 0;
}